Line cutting device

ABSTRACT

In a line cutting device of the type adapted to be mounted on the propeller shaft of a water-borne vessel for the purpose of cutting lines, ropes, nets, plastic bags or other debris which may foul the blades of a propeller on the shaft, a stationary cutting blade assembly is mounted so as to be restrained against rotation by cooperation with a shaft bearing. The stationary cutting blade assembly having a radially extending stationary cutting blade with an axially directed face and at least one circumferentially directed face defining a cutting edge therebetween. A rotatable cutting blade assembly is mounted for rotation with the propeller shaft and has at least one radially extending rotatable cutting blade thereon with an axially directed face and at least one circumferentially directed face defining a cutting edge therebetween. Upon rotation, the rotatable cutting blade assembly is arranged with respect to the stationary cutting blade assembly to provide a desired cutting action between the cutting edge of each rotatable cutting blade and the stationary cutting blade. Serrations on the cutting blades enhance the cutting action of the blades.

FIELD OF THE INVENTION

This invention relates to line cutting devices of the type adapted to bemounted on the propeller shaft of a water-borne vessel for the purposeof cutting lines, ropes, nets, plastic bags or other debris which mayfoul the blades of a propeller on the shaft.

BACKGROUND OF THE INVENTION

Such a device is disclosed in British Patent Specification No.GB-A-2139169, and comprises a stationary blade projecting radially froma ring and restrained against rotation by cooperation with a propellershaft bearing, and a pair of diametrally opposed rotatable bladesprojecting radially from another ring to be secured to the propellershaft. The blades have straight cutting edges on both sides lyingradially to the rings, so that the width of the blades increasesradially outwardly to form fan-shaped or dovetailed blades. At thedistal or radially outward free end of each blade integral ear portionsproject forwardly and rearwardly, in the direction of rotation. Thus theear portion on the leading edge of a rotating blade engages the earportion on the opposed edge of the stationary blade before the cuttingedges co-operate to shear a line therebetween. The intention of the earportions is to prevent jamming of the blades as they wear. As thecutting edges approach during rotation, a line caught in the spacetherebetween tends to slide radially outwardly along the cutting edgesuntil stopped by the ear portions, so that cutting usually takes placewith the line at the distal or radially outward ends of the cuttingedges. The moment of the cutting forces when cutting takes place thereis greater than if it takes place closer to the rings. In addition,cutting takes place through the full width of a line in one action andthis may prove difficult or impossible with large lines.

THE INVENTION

The object of the invention is to overcome this problem by providing aprogressive cutting of fouled lines which enables even large diameterlines to be successfully cut without jamming.

According to the invention, there is provided a line cutting device formounting around a propeller shaft between a shaft bearing and apropeller comprising a rotatable cutting blade assembly mountable forrotation with the propeller shaft and including at least one rotatablecutting blade extending generally radially of the propeller shaft andhaving a cutting edge provided between an axially directed face and acircumferentially directed face; and a stationary cutting blade assemblyadapted to be restrained against rotation by co-operation with the shaftbearing and including a stationary cutting blade extending generallyradially of the propeller shaft, having a cutting edge provided betweenan axially directed face and a circumferentially directed face andarranged for cutting action of its cutting edge with the cutting edge ofthe rotatable cutting blade on rotation of the propeller shaft with theaxially directed faces passing opposite each other during such rotation;wherein the cutting edge of the or each rotatable cutting blade and/orthe cutting edge of the stationary cutting blade is/are provided withserrations, and the cutting edges are shaped for cutting action of innerones of the serrations prior to such action of outer serrations oncontinued rotation of the propeller shaft.

The serrations tend to grip a fouled line and if it is larger than canbe fully cut by the first engaged serration(s), the outer serrations areengaged sequentially, progressively cutting the line.

Preferably, the axially directed faces of the stationary and rotatablecutting blades are flat and the respective circumferentially directedface(s) is/are provided with a tooth formation, whereby the said cuttingedge(s) is/are provided with the said serrations.

The tooth formation is conveniently of saw-tooth shape and thecircumferentially directed face(s) having this tooth formation is/areraked back from its cutting edge, whereby the cutting edge(s) is/areprovided with points.

Although cutting edges are preferably provided on both edges of blademembers, this may not be necessary if the device is to be mounted on apropeller shaft having a single direction of rotation.

Preferably, the saw-tooth shape is such as to be more sharply inclinedalong the portions outwardly inclined from the general radial directionof the blade member than along the portions inclined inwardly towardsthe general direction.

In the preferred embodiment, the rotatable cutting blade assemblyincludes a split hub adapted for clamping to the propeller shaft, thehub providing an annular groove at one end and a circular cylindricalseat at a mid portion for the stationary cutting blade assembly andhaving the rotatable cutting blade(s) radiating from its other end withits/their axially directed face(s) directed towards the circularcylindrical seat, and a split collar of greater radial dimension thanthe depth of the groove and clampable to the hub at the groove, wherebythe stationary cutting blade assembly is axially limited in the seat.

Conveniently, the stationary cutting blade assembly includes a splitring accommodatable at the circular cylindrical seat, and means foraxially splitting the ring for mounting to the seat prior to fitting ofthe collar to the hub.

THE DRAWINGS

To help understanding of the invention a specific embodiment thereofwill now be described by way of example and with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view, partly broken away, of a line cuttingdevice according to the invention fitted to a propeller shaft itselfmounted in shaft bearing;

FIG. 2 is an exploded view of the line cutting device of FIG. 1;

FIGS. 3 and 4 are end and side views of a rotatable cutting bladeassembly of the device of FIG. 2;

FIGS. 5 and 6 are end and side views of a stationary cutting bladeassembly of the device of FIG. 2;

FIGS. 7,8 and 9 are end, side and plan views of a striker block intendedto be secured to the propeller shaft bearing and to restrain thestationary cutting blade assembly against rotation; and

FIG. 10 is a cross-sectional view of a modified bearing element for theline cutting device.

THE EMBODIMENT

Referring to the drawings, a water-borne vessel (not shown) has apropeller shaft 10 (see FIG. 1) supported in a propeller shaft bearingin the form of a strut 12 with a boss 14 containing a journal for theshaft 10. On the aft side of the boss 14, the shaft 10 carries a linecutting device 16 including a rotatable cutting blade assembly 18 and astationary cutting blade assembly 20. The latter is restrained againstrotation by a striker block 22 secured to the boss 14. A propeller (notshown) will in use be fitted behind the line cutting device.

In the preferred embodiment illustrated and described, the stationarycutting blade assembly 20 includes a radially outwardly projectingstationary blade 24 whose opposed cutting edges 26 and 28 (see FIG. 2)are serrated. The rotatable cutting blade assembly 18 is secured to thepropeller shaft 10 to rotate therewith and includes three equally spacedradially outwardly projecting rotatable blades 30,32,34. The blades30,32,34 have opposed cutting edges 36 and 38,40 and 42,44 and 46,respectively, which are serrated. The blades narrow towards their outerends, so that, in operation, the radially inward portions of the cuttingedges co-operate in a cutting action, before the radially outwardportions thereof.

The stationary cutting blade assembly 20 comprises two half-rings 48 and50 having complementarily formed ends 52,54; 56,58 (see FIG. 5) whichinterlock to form a complete ring. Half ring member 48 has neck portions52',56', defining inwardly facing notches, which carry lugs 52",56". Theother half ring member 50 has neck portions 54',58', defining outwardlyfacing notches which carry the lugs 54",58". The lugs are of reducedradial dimension to fit the notches on axial assembly of the half ringmembers to each other. Half ring member 48 carries the blade 24 as anintegral part. The blade 24 has on its surface closer to the strut 12and boss 14, a forwards projection 60 of wedge tooth shape. Thisprojection engages in a bifurcated end 62 of the striker block 22mounted on the boss 14 (see FIG. 1).

The serrated shape of the cutting edges of the blades is achieved bygenerating saw-tooth formations on the circumferentially directed faces27,29,37,39,41,43,45,47 of the blades, each tooth terminating at itscutting edge in a serration (see FIG. 5).

The circumferentially directed faces curve towards each other from theirinner to their outer ends. The result is that as each rotatable blade30,32,34 passes the stationary blade 24, the radially inner serrationspass in a cutting action well in advance of the radially outer teeth.The circumferentially directed faces formed with the saw teeth are rakedback from the cutting edges to provide points26',28',36',38',40',42',44',46' at the cutting edges to dig into anyline or other matter to be cut. The saw teeth on the different bladesare provided at equivalent radial positions, whereby the points on thestationary blade align with the points on each rotating bladeapproaching the stationary blade. The stationary blade 24 and therotating blades 30,32,34 have flat axially directed faces24",30",32",34", which pass opposite each other during rotation. Thefaces 30",32",34" remain spaced from the face 24" by the thrust bearingthickness of bearing elements 104, described below.

The rotatable cutting blade assembly 18 includes a hub comprised of twohalf hub members 64,66 having opposed faces 68,70 (see FIG. 3). Alignedpairs of holes 72,74; 76,78 in the half hub members 64,66 open throughthe faces 68,70 and bolts 80,82 passed through the holes 72,76 engage inthe holes 74,78 which are threaded to enable the half hub members to bejoined together to form a complete hub tightly engageable upon thepropeller shaft 10. The half hub member 64 integrally carries two blades30,32. The half hub member 66 integrally carries one blade 34. The hub64,66 extends forwardly to provide an annular groove 84 for anadditional pair of half collar members 86,88 which have opposed faces90,92 intended to be set at right angles to the faces 68,70, whereby thehalf collar members 86,88 each bridge one of the circumferential jointsin the hub at the faces 68,70 and bring the half hub members 64,68--andtheir blade members 30,32,34--into axial alignment. The additional halfcollar members 86,88 are joined together by two bolts 94,96 in a mannersimilar to the half hub members 64,66. The central portions of the halfhub members 64,66, together with the half ring members 86,88, thusprovide an axially limited circular cylindrical seat 98 for thestationary cutting blade assembly 20.

Each of the half ring members 48,50 has three recesses 100 on each faceof the member. Each recess 100 receives a boss 102 integral with one armof a combined journal and thrust bearing segment 104 of L-shapedcross-section made of an anti-friction plastics material such asTUFFCOTE-MOLY. The half ring members 48,50, complete with their bearingsegments 104, are assembled and carried on the seat 98 provided on thehalf hub members 64,66.

The sequence of mounting on the propeller shaft 10 is for the half hubmembers 64,66 to be offered up to the shaft and the bolts 80,82 looselyengaged. One of the half ring members 48,50--with its bearingsegments--is positioned at the seat 98 and the other offered up so thatthe complementary end formations 52,54; 56,58 engage axially. The halfcollar members 86,88 are then engaged in their annular groove 84 withthe bolts 94,96 being loosely engaged. Tightening of bolts 80,82 andthen of bolts 94,96 secures the rotatable cutting blade assembly tightlyon the shaft 10, with the stationary cutting blade assembly journalledthereon.

The striker block 22 has a base member 106 (see FIG. 7) which has acurvature substantially that of the boss 14. The block 22 has threefixing screw holes 108 (see FIG. 9) along its centre line via which itis secured to the boss 14 with tension bolts not shown. Three adjustablecompression studs 110 are provided in lugs to either side and one end ofthe striker block to provide adjustable three legged support against thehub for the case where the block 22 requires to be spaced slightly fromthe boss 14. The vee-shaped bifurcated end 62 of the striker block 22projects from the back of the base member 106 and is aligned to andengages with the forward wedge projection 60 on the blade 24. To providefor contact substantially midway along the radial extent of theprojection 60, its faces are barrelled.

In use, the rotatable cutting blade assembly 18 rotates with thepropeller shaft and if a line becomes entangled therewith, one of therotating blades 30,32,34 catches it against the sawteeth serrationsthereof and carries it into contact with the stationary blade 24.Continued relative rotation causes the opposed cutting edges of theblades to sever the line. If the line is large, the radially innersawtooth serrations of the rotating blade grip the fouled line so thatwhen it is engaged by the radially inner sawtooth serrations of thestationary blade, it is divided into portions between radiallysuccessive serrations and the portions progressively cut by thesequentially engaging serrations.

FIG. 10 shows alternative bearing elements 204. Each has a thrust flange205 and a journal ring 206, the elements being of 360° extent with oneradial split 207 each. The journal rings are of a size to fit tightlywithin the half ring members 48,50 when assembled. The thrust flanges205 are slightly dished as shown by their dimension 208 in their freestate being slightly larger than the thrust gap between the stationaryand rotatable cutting blade assemblies. Thus when the cutting device isassembled, any slop between the assemblies is taken up and theprojection wedge 60 does not knock in the bifurcated end 62 of thestriker block. The elements 204 are radially split to allow fitting ofthe line cutting device without pulling off the propeller.

Whilst one stationary blade is preferred, two or more may be used on thestationary cutting blade assembly. In the same way, one, two, four ormore rotatable blades may be used on the rotatable cutting bladeassembly. The cutting edges need be on one side only of the blades ifthere is no question of reverse rotation on the shaft.

I claim:
 1. A line cutting device for mounting around a propeller shaftbetween a shaft bearing and a propeller comprising:A. a rotatablecutting blade assembly mountable for rotation with the propeller shaftand including at least one rotatable cutting blade extending generallyradially of the propeller shaft, each said rotatable cutting bladehaving an axially directed flat face and a circumferentially directedface, said faces of each cutting blade defining a cutting edgetherebetween; and B. a stationary cutting blade assembly adapted to berestrained against rotation by co-operation with the shaft bearing andincluding a stationary cutting blade extending generally radially of thepropeller shaft, said stationary cutting blade having an axiallydirected flat face and a circumferentially directed face, said facesdefining a cutting edge therebetween, said stationary cutting bladeassembly being arranged for cutting action of its cutting edge inconjunction with the cutting edge of each rotatable cutting blade onrotation of the propeller shaft with the axially directed faces passingopposite each other during such rotation, said circumferentiallydirected face of each rotatable cutting blade and said circumferentiallydirected face of said stationary cutting blade extend away from eachother from their radially inner ends to the outer ends when in relativecutting position to each other; and C. serrations included on eachcutting edge of each rotatable cutting blade and the cutting edge of thestationary cutting blade, each respective circumferentially directedface is provided with at least one tooth formation thereon, each toothformation has a saw-tooth shape and each circumferentially directed facehas its tooth formation raked back from its cutting edge, whereby eachcutting edge is provided with points, the saw-tooth formations on eachface being provided at equivalent radial spacing, whereby the points onthe stationary cutting blade act at the same radius as the equivalentpoints on the rotatable cutting blade, the cutting edges being shapedfor cutting action of radially inner ones of the serrations prior tosuch action of radially outer ones of said serrations on continuedrotation of the propeller shaft.
 2. A line cutting device as claimed inclaim 1, wherein the circumferentially directed faces of each cuttingplate curve towards each other from their radially inner end to theirouter ends.
 3. A line cutting device is claimed in claim 2, wherein therotatable cutting blade assembly includes a split hub adapted forclamping to the propeller shaft, the hub having an annular groove at oneend and a circular cylindrical seat at a mid portion for the stationarycutting blade assembly and having each rotatable cutting blade radiatingfrom its other end with its axially directed face directed towards thecircular cylindrical seat, and a split collar of greater radialdimension than the depth of the groove, clampable to the hub at thegroove; whereby the stationary cutting blade assembly is axially limitedin the seat.
 4. A line cutting device as claimed in claim 3, wherein thestationary cutting blade assembly includes a split ring accommodatableat the circular cylindrical seat, and means for axially splitting thering for mounting to the seat prior to fitting of the collar to the hub.5. A line cutting device as claimed in claim 4, wherein the split ringcomprises two half ring members, one half ring member having at its endsreduced radial dimension lugs connected to the member by neck portionsdefining inwardly facing notches, the other half ring member having atits ends reduced radial dimension lugs connected to the member by neckportions defining outwardly facing notches, the ring being assembledaxially by fitting the lugs of one member into the notches of the othermember.
 6. A line cutting device as claimed in claim 5, wherein thesplit ring carries moulded, combined thrust and journal bearingelements.
 7. A line cutting device as claimed in claim 6, wherein thebearing elements have thrust portions which are axially dished to takeup axial slack between the stationary cutting assembly and the rotatablecutting assembly.
 8. A line cutting device as claimed in claim 7,wherein the stationary cutting blade assembly is restrained by anintegral projection engaging a striker block, the striker block beingsecurable by central tension elements and spaced compression elements.9. A line cutting device as claimed in claim 3, wherein the stationarycutting blade assembly is restrained by an integral projection engaginga striker block, the striker block being securable by central tensionelements and spaced compression elements.
 10. A line cutting device asclaimed in claim 1, wherein the stationary cutting blade assembly isrestrained by an integral projection engaging a striker block, thestriker block being securable by central tension elements and spacedcompression elements.
 11. A line cutting device for mounting around apropeller shaft between a shaft bearing and a propeller comprising:A. arotatable cutting blade assembly mountable for rotation with thepropeller shaft and including at least one rotatable cutting bladeextending generally radially of the propeller shaft, each said rotatablecutting blade having an axially directed face and two circumferentiallydirected faces, said faces of each cutting blade defining cutting edgestherebetween, the circumferentially directed faces of each rotatablecutting blade curve toward each other from their radially inner ends totheir outer ends; and B. a stationary cutting blade assembly adapted tobe restrained against rotation by co-operation with the shaft bearingand including a stationary cutting blade extending generally radially ofthe propeller shaft, said stationary cutting blade having an axiallydirected face and two circumferentially directed faces, said facesdefining cutting edges therebetween, the circumferentially directedfaces of said stationary cutting blade curve toward each other fromtheir radially inner ends to their outer ends, said stationary cuttingblade assembly being arranged for cutting action of its cutting edge inconjunction with the cutting edge of each rotatable cutting blade onrotation of the propeller shaft with the axially directed faces passingopposite each other during such rotation; C. serrations included on atleast one cutting edge of each rotatable cutting blade and the cuttingedge of the stationary cutting blade, the cutting edges being shaped forcutting action of radially inner ones of the serrations prior to suchaction of radially outer ones of said serrations on continued rotationof the propeller shaft.
 12. A line cutting device for mounting around apropeller shaft between a shaft bearing and a propeller comprising:A. arotatable cutting blade assembly mountable for rotation with thepropeller shaft and including at least one rotatable cutting bladeextending generally radially of the propeller shaft, each said rotatablecutting blade having an axially directed face and a circumferentiallydirected face, said faces of each cutting blade defining a cutting edgetherebetween; B. a stationary cutting blade assembly adapted to berestrained against rotation by co-operation with the shaft bearing andincluding a stationary cutting blade extending generally radially of thepropeller shaft, said stationary cutting blade having an axiallydirected face and a circumferentially directed face, said faces defininga cutting edge therebetween, said stationary cutting blade assemblybeing arranged for cutting action of its cutting edge in conjunctionwith the cutting edge of each rotatable cutting blade on rotation of thepropeller shaft with the axially directed faces passing opposite eachother during such rotation; C. the rotatable cutting blade assemblyincludes a split hub adapted for clamping to the propeller shaft, thehub having an annular groove at one end and a circular cylindrical seatat a mid portion for the stationary cutting blade assembly and havingeach rotatable cutting blade radiating from its other end with itsaxially directed face directed towards the circular cylindrical seat,and a split collar of greater radial dimension than the depth of thegroove, clampable to the hub at the grove; whereby the stationarycutting blade assembly is axially limited in the seat; and D. serrationsincluded on at least one cutting edge of each rotatable cutting bladeand the cutting edge of the stationary cutting blade, the cutting edgesbeing shaped for cutting action of radially inner ones of the serrationsprior to such action of radially outer ones of said serrations oncontinued rotation of the propeller shaft.
 13. A line cutting device formounting around a propeller shaft between a shaft bearing and apropeller comprising:A. a rotatable cutting blade assembly mountable forrotation with the propeller shaft and including at least one rotatablecutting blade extending generally radially of the propeller shaft, eachsaid rotatable cutting blade having an axially directed face and acircumferentially directed face, said faces of each cutting bladedefining a cutting edge therebetween; B. a stationary cutting bladeassembly adapted to be restrained against rotation by co-operation withthe shaft bearing and including a stationary cutting blade extendinggenerally radially of the propeller shaft, said stationary cutting bladehaving an axially directed face and a circumferentially directed face,said faces defining a cutting edge therebetween, said stationary cuttingblade assembly being arranged for cutting action of its cutting edge inconjunction with the cutting edge of each rotatable cutting blade onrotation of the propeller shaft with the axially directed faces passingopposite each other during such rotation; C. thrust bearing meansbetween said rotatable cutting blade assembly and said stationarycutting blade assembly for limiting axial approach of said rotatablecutting blade and said stationary cutting blade, whereby said axiallydirected face of said rotatable cutting blade remains spaced from saidaxially directed face of said stationary cutting blade; D. serrationsincluded on at least one cutting edge of each rotatable cutting bladeand the cutting edge of the stationary cutting blade, the cutting edgesbeing shaped for cutting action of radially inner ones of the serrationsprior to such action of radially outer ones of said serrations oncontinued rotation of the propeller shaft.
 14. A line cutting device formounting around a propeller shaft between a shaft bearing and apropeller comprising:A. a rotatable cutting blade assembly mountable forrotation with the propeller shaft and including at least one rotatablecutting blade extending generally radially of the propeller shaft, eachsaid rotatable cutting blade having an axially directed face and acircumferentially directed face, said faces of each cutting bladedefining a cutting edge therebetween; B. a stationary cutting bladeassembly adapted to be restrained against rotation by co-operation withthe shaft bearing and including a stationary cutting blade extendinggenerally radially of the propeller shaft, said stationary cutting bladehaving an axially directed face and a circumferentially directed face,said faces defining a cutting edge therebetween, said stationary cuttingblade assembly being arranged for cutting action of its cutting edge inconjunction with the cutting edge of each rotatable cutting blade onrotation of the propeller shaft with the axially directed faces passingopposite each other during such rotation, said circumferentiallydirected face of each rotatable cutting blade and said circumferentiallydirected face of said stationary cutting blade curve away from eachother from their radially inner ends to the outer ends when in relativecutting position to each other; and C. serrations included on at leastone cutting edge of each rotatable cutting blade and the cutting edge ofthe stationary cutting blade, the cutting edges being shaped for cuttingaction of radially inner ones of the serrations prior to such action ofradially outer ones of said serrations on continued rotation of thepropeller shaft.
 15. A line cutting device for mounting around apropeller shaft between a shaft bearing and a propeller comprising:A. arotatable cutting blade assembly mountable for rotation with thepropeller shaft and including at least one rotatable cutting bladeextending generally radially of the propeller shaft, each said rotatablecutting blade having an axially directed face and a circumferentiallydirected face, said faces of each cutting blade defining a cutting edgetherebetween; B. a stationary cutting blade assembly adapted to berestrained against rotation by co-operation with the shaft bearing andincluding a stationary cutting blade extending generally radially of thepropeller shaft, said stationary cutting blade having an axiallydirected face and a circumferentially directed face, said faces defininga cutting edge therebetween, said stationary cutting blade assemblybeing arranged for cutting action of its cutting edge in conjunctionwith the cutting edge of each rotatable cutting blade on rotation of thepropeller shaft with the axially directed faces passing opposite eachother during such rotation, said circumferentially directed face of eachrotatable cutting blade and said circumferentially directed face of saidstationary cutting blade extend away from each other from their radiallyinner ends to the outer ends when in relative cutting position to eachother; and C. serrations included on at least one cutting edge of eachrotatable cutting blade and the cutting edge of the stationary cuttingblade, the cutting edges being shaped for cutting action of radiallyinner ones of the serrations prior to such action of radially outer onesof said serrations on continued rotation of the propeller shaft.